This book serves as an up-to-date and accessible introduction to new language acquisition research. Teaching English as a second language (ESL) / foreign language (EFL) to non-English speaking students in relation to the use of learners’ first language in foreign classroom has been a debatable issue among practitioners and researchers. This study seeks to contribute to that debate and focuses on the EFL context since little research has been conducted in this area. In particular, this study investigates the role of the first language in foreign classrooms from the perspective of EFL teachers. Also, it highlights the theories and methods of second language acquisition and the role of teachers’ beliefs, attitudes and experiences in second and foreign language learning. Different methods of data collection have been used in this study which includes questionnaires, interviews and classroom observations. Some interesting data and themes have emerged from this study in relation to the use of first language in foreign language classroom. This book should be especially useful to ESL and EFL researchers, practitioners and teachers.